Rats

Rats are a significant pest for human beings. They destroy crops and try to live in farms and human habitats bringing with them immense damages to the economy of countless number of human beings be it directly or indirectly. Direct damages that can be clearly seen are the damages caused by rats eating crops of human beings in plantations and fields as well as causing contamination in the storage areas, transport and processing stage of crops until crops are in the hands of consumers. Apart from agricultural crops, animal food and produce of animals as well as consumer products of human beings are also damaged by rats. Moreover, rats are carriers of several diseases that affect human beings and pets for instance leptospirosis, murine thyphus, scrub thyphus, plaque and digestive diseases. Indirect diseases result from rats biting to exercise their teeth for instance various objects, electrical wires, electronic devices or even construction materials in the building which may cause short circuits in case rats bite electric wires. Such incident is also harmful to lives and properties of human beings. Moreover, rats digging and living under buildings and along the ridges, canal ridges or in the drainage pipes cause building floors and river banks to sink or drainage pipes to be blocked. These damages are incalculable. Moreover, nowadays, safe food industries need to take into account all steps of the production procedure. In each step, there needs to be certain practices and production control for the products to be of good quality and all steps of production process need to pass sanitary standards. Hence rat prevention and eradication in a correct and systematic manners are needed. This is to avoid contaminations from rat excrement or carcasses of rats in the production line that may cause an infectious disease to be transferred from rats to human beings.

Biological and Ecological Features of Rats

Rats are small mammals in cylindrical shape. A rat has four legs. Each of its front foot has four toes that function like hands while each of its back foot has five toes that are bigger. Its head and body are covered with hair. A rat has huge eyes and ears. Its tail is as long as or longer than its body length. A rat has 2 pairs of incisors that continue to grow over the course of its life. Hence rats always bite both food and objects. Rats have excellent senses. They go look for food at night but sometimes, when there is a lack of food or there is an exceeding number of rat population, some rats have to look for food during the day. Moreover, they have very quick sense of taste allowing them to detect any strange or toxic substance in the food easily. Hence, rats will remember the baits and the latter will be in their memory for 2-5 months. Rats are also able to emit and hear the sound which has the frequency as high as 45,000 rounds per minute (45 Khz). On the other hand, rats’ vision is not good when compared to human eyes. This is because the structural system in terms of vision and light sensor of rats has been made appropriate to night-time vision as rats find food at night. They only see images in black and white. Rats are philoprogenitive as they can breed almost throughout the year. Each year, rats give birth to several litters. Some calculate that in a year, a pair of rats is able to breed more than 1,000 rats.

Factors that are important to the life of a rat

  • Food and water sources
  • Habitats
  • Natural enemies
  • Population density
  • Distance to food

Significant types of rat in terms of Public Health

1. Norway Rat, Brown Rat, Harbour Rat or Sewer Rat

  • Scientific name: Rattus Norvegicus (Berkenhout, 1769)
  • Several names have been used depending on their habitats or food sources for instance, pipe rat, rubbish rat, port rat and Lau rat.
  • This is the largest type of rat in this family with weight of approximately 200-500 grams
  • They are fierce and arrogant.
  • They eat all types of food as well as leftovers that are of good conditions and new types of food.
  • They like to live in the ground, under the rubbish, earth cavity, under cracks in the floor, space under a house or in sewage pipes near communities like in markets.
  • They live in communities with pecking order. Leaders are usually strong male rats.
  • They are found in every city area. They may also be found in agricultural areas adjacent to large communities.
  • They are carriers of various critical diseases to humans and pets.

2. Roof Rat, Ship Rat or House Rat

  • Scientific Name: Rattus rattus (Linnaeus, 1758)
  • They are also called black rats, roof rats and ship rats.
  • They tend to live on the trees, on ceilings of buildings, barns and agricultural areas.
  • They like to eat fruit, vegetables and plant seeds more than meat.
  • They avoid fights with other rats. They do not like living in large groups.
  • Their hair colours are diverse depending on the areas that they are found. They weigh around 90-250 grams. Females have 2 pairs of breast at its chest and 3 pairs at its stomach.

3. Polynesian Rat or Burmese House Rat

  • Scientific Name: Rattus Exulans (Peal, 1817)
  • They tend to live in dry areas in houses especially in the kitchen, storage room, in a cupboard, drawers and barns.
  • They like to eat fruit, vegetables, plant seeds and meat.
  • They like to climb. They avoid fights with other rats and they do not like living in large groups.
  • They are the smallest among the family of Rattus. Their weights are between 27-60 grams. They have large eyes and ears. Their tails are longer than their heads and are of the same colour throughout. Their hairs at the back are of dark brown in colour and their stomachs are grey.

4. House Mouse

  • Scientific Name: Mus Musculus (Linnaeus, 1766).
  • They tend to live in dry areas in houses especially in the kitchen, storage room, in a cupboard, drawers and barns.
  • They like to eat fruit, vegetables, plant seeds and meat.
  • They like to climb. They get scared easily. They go out to find food at night. They like to explore new environments everyday. They avoid fights with other types of rat.
  • As of now, these rats are not found in Thailand. They are smaller than European house mouses but have similar hair colour. Their hair colour on the top and at their stomachs is dark. Their backfoot hairs are black except the ends of their nails which are white. They have small teeth and shallow faces.

 

rat-1
Norway Rat
rat-2
Roof Rat
rat-3
Polynesian Rat
rat-4
House Mouse

 

Methods of Control

1. Hygiene and environmental sanitation

  • Adjust the environment in plantations for instance making small field ridges and eradicating pests. Human habitats, animal farms and enterprises must comply with principles of good environmental sanitation.
  • Control habitats of rats.
  • Prevent rats from entering buildings

2. Biological Control

  • Use predators for instance barn owls, rat-eating snakes or mongooses.
  • Train animals such as cats and dogs to chase or eradicate rats.
  • Use parasites or diseases found in rats to kill rats for instance using protozoa to kill rats using Sarcocystis Singaporensis or a protozoa parasite that causes disease that kills a rat.

3. Mechanical Control

  • Reduce the number of rats in plantations of economic crops and in buildings or houses by digging up rats’ holes or using mouse cages, adverse mouse traps and sticky mouse traps.

4. Physical Control

  • Chasing rats from the areas that need to control using ultrasound generator or sound wave or electromagnetic waves.
  • Killing rats using electric fences or building fences along the areas where small plants are being grown with smooth galvanised iron, cellocrete and light-reflecting foils.

5. Chemical Control

  • Fumigants are suitable to use to eradicate rats in confined spaces such as goods storage, and freight ship. Substances used are for instance fumigants include methyl bromide and alluminium phosphine.
  • Rodenticides may be divided into 2 types according to the time used to kill rats;
    • 1. Acute Poisoned Rodenticides They react immediately after rats take these in single dose or in a short period of time. They destroy the nervous system causing rats to become paralysed and die in the end. They destroy liver, kidneys and cause heart failure or paralysis. Rats will die within the period of 3 hours to 1 day. These chemicals are usually used in high concentration doses. For instance, there is zinc phosphide 0.8-1%. However, Ministry of Public health has announced that the substance is the hazardous substance number 4 according to Hazardous Substance Act B.E.2535 (1992). It is forbidden to produce, import, export or possess such substance.
    • 2. Chronic Poisoned Rodenticides or Anticoagulant Rodenticides These are rodenticides that need to be consumed several times by rats. Then the toxin will accumulate in the body of a rat to the point that kills it through anticoagulant process causing blood to flow out of capillaries and openings in the body along the wounds. Blood will clot in various organs in the body. Then the rat will die within 3-15 days. Ready-made poisoned bait has the concentration of reactants between 0.005% – 0.1%.

6. Integrated Control

This is the combination of the above methods at appropriate time and place to achieve the highest efficiency for a long period of time with low expenses. They are also environmentally friendly.

It is widely known that rats are smart and they can avoid methods of humans that attempt to control and reduce the number of rats. Hence, the prevention and eradication of rats need to combine several methods at the same time to be successful. This is also called an Integrated Rodent Pest Management. This should be used as a strategy to prevent, control and eradicate rats. This is the most important method than any other. The procedure is as follows;

Step 1: Survey the number and traces of rats as well as evaluate the issue of rats in the area and make the map of the area that needs to be controlled by indicating containers for toxic baits. Then an operating plan to prevent and eradicate rats needs to be made.

Traces of rats that should be observed in the areas that need to be controlled include footprints, dungs, urine trace, hair, path, sound, body or carcasses of rats as well as biting traces on various food and objects.

Step 2: Prevent and eradicate rats according to the planned strategy.

Step 3: Assess the results following the prevention and eradication of rats by surveying traces and number of rats regularly and analyse to compare results.

Step 4: Survey traces of rats regularly. One should operate the prevention and eradication of rats at least every 3-6 months.